1. Field of the Invention
The present invention relates to a side door structure applicable to a vehicle body of which side openings are covered by front doors swingably supported by door hinges located at the front of the front doors and by rear doors swingably supported by door hinges located at the rear of the rear doors.
2. Description of the Related Art
There exists a conventionally known side door structure of a vehicle of which front doors and rear doors covering side openings in a vehicle body are opened frontward and rearward, respectively, as described in Japanese Unexamined Patent Publication No. 2001-138864, for example. In this side door structure (hereinafter referred to as the two-way opening side door structure), the front doors are swingably supported by door hinges located at the front of the front doors and the rear doors are swingably supported by door hinges located at the rear of the rear doors so that they can be opened frontward and rearward, respectively.
The two-way opening side door structure of the vehicle disclosed in the above-cited Japanese Unexamined Patent Publication No. 2001-138864 is built as follows. When opening a rear door 4a, an occupant first undoes a door lock of a front door 2a and opens the front door 2a to a specific angle as shown by imaginary lines in FIG. 14 to release the front and rear doors 2a, 4a from their interlocked state. Then, the occupant swings the rear door 4a from a closed position to an open position.
Generally, upper portions of side doors (front and rear) of the vehicle are inwardly inclined as viewed from the front of the vehicle so that upper ends of the side doors are located more or less inward toward a center line of the vehicle body largely for design-related reasons. When the front and rear doors 2a, 4a of which upper portions are inwardly inclined are swingably supported by vertically mounted hinge pins 17a and 12a, respectively, as shown in FIG. 14, a rearmost part of the upper end of the front door 2a swings slightly rearward whereas a forwardmost part of the upper end of the rear door 4a swings slightly frontward in an initial stage of opening the respective doors 2a, 4a. This is because the upper ends of the front and rear doors 2a, 4a are positioned inward toward the center line of the vehicle body with respect to longitudinal axes of the hinge pins 17a, 12a. 
In addition, the front and rear doors 2a, 4a are installed in such a manner that a rear end of the front door 2a and a front end of the rear door 4a overlap each other by a specific distance OL. Therefore, a swing trajectory of the rear end of the front door 2a and a swing trajectory of the front end of the rear door 4a produced as the respective doors 2a, 4a are opened and closed inevitably overlap over a large area “A” as illustrated (hatched in FIG. 14).
In this structure, the front end of the rear door 4a is apt to interfere with the rear end of the front door 2a when the rear door 4a is opened and, therefore, the occupant has to open the rear door 4a after widely opening the front door 2a to prevent this interference between the front and rear doors 2a, 4a. The conventional two-way opening side door structure has this problem concerning operational ease.